This invention relates to an actuator, and in particular to an actuator suitable for use in association with the landing gear of an aircraft, although the actuator may be used in other applications.
The landing gear of an aircraft is typically driven between its stowed and deployed positions by a primary actuator. The weight of the landing gear is sufficient that, during deployment, the primary actuator serves primarily to control the speed of movement of the landing gear under the force of gravity towards the deployed position, the primary actuator also serving to drive the landing gear back towards the stowed position after use. A hinged stay serves to support the landing gear, when at its deployed position, and an over-centre hinged strut is typically provided to hold or lock the landing gear in its deployed position, a spring arrangement being used to drive the strut to its over-centre, locked position.
Due to the provision of the over-centre strut, the primary actuator is unable, alone, to drive the landing gear from its fully deployed position to its stowed position, and a secondary actuator is typically provided to drive the strut against the spring biasing thereof to its over-centre position, thereby releasing the locking effect of the over-centre strut and permitting the primary actuator, in conjunction with further movement of the secondary actuator, to then drive the landing gear to its stowed position.
In such an arrangement there is the risk that failure of the secondary actuator, resulting in jamming thereof, may prevent the strut from reaching its fully deployed, over-centre locked position, thus preventing the landing gear from being locked in its fully deployed position. Obviously, if the landing gear cannot be locked in its deployed position, the ability of the aircraft to undertake a safe landing may be impaired. It may also prevent stowing of the landing gear, but this is considered to be less problematic as, provided the landing gear is still able to return to, and be locked in, its fully deployed position, the aircraft is still able to land safely, whereon appropriate repairs to the landing gear can be undertaken.